1. Field of the Invention
The present invention relates to an opening/closing mechanism provided for a liquid path for a liquid or a gas, and relates in particular to a liquid path opening/closing mechanism that can control the movement of a small quantity of liquid.
The following explanation will be given for a liquid path opening/closing mechanism that is used for the ink supply path of an ink-jet recording apparatus, such as an ink-jet printer, a facsimile machine or a copier. However, the present invention is not limited to this field, and pertains to a liquid path opening/closing mechanism that can also be employed for pharmaceuticals (including liquids, liquids in which powder has been dispersed, and gases), or for liquids having a high degree of purity (e.g., super pure water).
Furthermore, the liquid path opening/closing mechanism can also be used for air or other liquids (detergents, juice, spices or seasonings). Since the liquid path opening/closing mechanism is safe and light because in operation little pressure is required, and since power consumption is low, this mechanism is especially preferable for small toys (toy robots), a market that it is predicted will expand.
2. Related Background Art
For the following explanation, an ink-jet recording field is employed.
There are two types of ink-jet recording apparatuses: a continuous type and an on-demand type.
An ink-jet recording apparatus of a continuous type sequentially ejects ink through nozzles at high pressure, and changes the ink ejection direction on the fly en route to perform printing or to form images.
In a recording apparatus, an opening/closing mechanism is provided along an ink channel that supplies and halts the supply of ink at the start and at the end of printing. A large high pressure opening/closing mechanism, i.e., about 20 mm wide, 30 mm high and 20 mm long, is constructed of a strong material, such as metal, and has a complicated internal arrangement.
As is disclosed in Japanese Patent Application Laid-open No. 3-101944, since an on-demand ink-jet recording apparatus is designed for the ejection of ink droplets by an ink-jet ejection device, high pressure need not be exerted on the ink, and ink need only be supplied from an ink tank to an ink-jet head. Further, ink is supplied from the ink tank to the ink-jet head under a slight negative pressure (by using a head difference or providing a negative pressure exertion mechanism for the ink tank), so that ink leakage at the ink-jet head is prevented.
Therefore, for an on-demand arrangement, an ink channel that connects an ink tank to an ink-jet head need not be opened or closed to supply ink, but rather, all that is required is that a pipe be permanently provided, so that the ink-jet head can use head difference to suck up the necessary amount of ink. Either this, or merely an ink cartridge method is required in which an ink absorption member is stored as a negative pressure exertion member in an ink tank and ink is retained in and supplied from the member.
However, in recent applications wherein ink-jet recording apparatuses are employed to record high-resolution images, such as photo images, instead of simply supplying black and three other colors, Y (yellow), M (magenta) and C (cyan), six or seven different ink colors, including dark and light shades, and a special color or a processing liquid are required.
In addition, since the number of prints increases in consonance with an increase in the printing speed, a large amount of ink is required, and accordingly, a large ink tank is a necessity, while the current trend, in accordance with popular demand, is for recording apparatuses to be reduced in size, and for, in the arrangement of the components in the recording apparatus, the ink tank to be located higher than the ink-jet head, although conventionally such an arrangement is not employed.
Furthermore, according to one method, ink is stored separately from the ink-jet head in a large ink container, and a pipe is employed to carry the ink from the container to the ink-jet head.
According to this method, there is a need for ink to be stored in the liquid state at a location higher than the ink-jet head, and to be supplied as needed.
However, a small ink flow controller and associated parts are required, so that the configuration can cope with a small ink-jet head and seven colors of ink, for example.
A practically sized controller for this purpose is one that is about 15 mm in height, 15 mm in length and 15 mm in width, or smaller.
When a large amount of ink stored in an ink tank is to be supplied along a tube or a pipe to an ink-jet head, the ink flow controller must be located at the outlet port of the ink tank or along the route followed by the ink flow.
However, since in this configuration the ink-jet head is fixed, for the following reasons it is not always preferable for this configuration to be employed for a serial printing system in which the ink-jet head is moved horizontally.
Due to the inertia when an ink-jet head is moved horizontally, pressure fluctuation occurs such that more ink is supplied than is necessary and a negative pressure is generated on the suction side thereby making the ejection of ink from the ink-jet head unstable. It was found that no particular problem arose during the conventional printing of letters or characters, but that when a high-resolution image, such as a photo image, was printed, a slight variance or deterioration in printing quality was noted.
This problem is disclosed in detail in Japanese Patent Application Laid-open No. 7-251507. According to the disclosed configuration, an opening/closing device for controlling the flow of ink is located on the side of an ink-jet head, adjacent to the outlet of a pipe. For this configuration, it is preferable that the opening/closing device for controlling the ink flow be light and compact, and that it exhibit a superior response property. However, the valve of the opening/closing device in Japanese Patent Application Laid-open No. 7-251507 is opened or closed either in the same direction as or in the opposite direction to the flow of ink, although the structure of the opening/closing device is not described. Further, according to this publication, when the size of the opening/closing device is increased the size of the recording apparatus is also increased.
The objective of the invention is to provide an opening/closing device for an ink flow path that resolves the above problem.
Thus, the present inventor purposely searched for an ink joint having an opening/closing device that would satisfy the above described requirements, but found none. And then, because they had to prepare a conventional ink joint, the present inventors examined available conventional techniques that could be used for the production of an ink joint, but again, could not find a desirable technique.
Conventional techniques applied for the production of opening/closing devices are disclosed in Japanese Patent Application Laid-open No. 9-089146, No. 7-243542 and No. 5-026262. However, none of the devices described in these publications is an ink joint, equipped with an opening/closing device, that is small and light enough for four to seven of them to be mounted on an ink-jet head.
In FIG. 5 is shown a conventional, comparatively simply structured opening/closing device that is disclosed in Japanese Patent Application Laid-open No. 7-243542, and in FIG. 6 is shown another conventional, comparatively simply structured opening/closing device that is disclosed in Japanese Patent Application Laid-open No. 9-089146.
In FIG. 5, the opening/closing device is employed as a valve for preventing backflow in a water pipe, etc., and as is shown in FIG. 5, the valve comprises: a case 68, a spring 62, a moving core 63, a coil 61, a valve rod 70, an operating valve body 71, and a coil support member 72.
In FIG. 6, the opening/closing device is a solenoid valve used for an oxygen cylinder for continuously supplying an adequate volume of oxygen to a hospital ward, etc., while an empty oxygen cylinder is being exchanged for a new, full cylinder. The solenoid valve comprises a coil 61, a spring 62, a valve rod 63, an auxiliary shaft 64, a sealing member 65, a ring-shaped iron core 66, an auxiliary member 67 and a case 68.
Further, in Japanese Patent Application Laid-open No. 57-026262, for which no drawing is supplied, a structure is disclosed for a valve driving mechanism having the improved response property of a fuel supply injector used for an automobile engine.
Very high pressures are used with these, conventional opening/closing mechanisms, and the structural members must not only be strong but must permit a high flow rate for the liquid that is used. Further, these mechanisms may be formed by machining metal castings or by directly machining masses of metal, and they are large structures for which reductions in size are not requested.
It is one objective of the present invention to provide a small, light, reliable opening/closing device having a simple structure that can not be implemented by the prior art.
As the main objective, it is demanded that the air flow rate and timing be controlled so only a comparatively low pressure is required for the precise supply of ink or another liquid. As previously described, a compact structure, light and simple, is preferable. At the least, one opening/closing device portion for the structure should have a weight equal to or less than 30 g and a size equal to or smaller than 4 cm3, and should facilitate the supply and discharge of ink or another liquid.
Therefore, as the result of a purposeful study, it was found that in order to provide a compact structure, using a solenoid, that could provide the above function, a drive shaft must preferably be operated in a magnetic field, and for a compact structure, the magnetic flux density must be increased. Accordingly, it is necessary for a closed magnetic circuit to be formed to contain the magnetic flux, so that its external dispersion is prevented. As a result, an innovative structure was provided wherein the case of a solenoid valve was formed of a highly permeable material, a coil was located inside the case, and the drive shaft and the ink flow path were defined inside the coil.
Since the case and the drive shaft are about 10 mm in diameter and are equal to or less than 10 mm in height, it is impossible to reduce manufacturing costs when a normal cutting process is employed.
Therefore, to reduce manufacturing costs, a metal deep-drawing process was used for the case, composed of a highly permeable material, and cold forging was used for the drive shaft. Further, to reduce power consumption, wire having a diameter of 50 to 100 xcexcm was employed as the winding for the coil, and a greater magnetic flux density was attained by increasing the number of windings. As a result, it was possible to manufacture, at low cost, a small valve that could open or close an air or liquid flow path under a pressure of approximately two atmospheres, and that had a power consumption of only 0.3 to 1.5 W.
Further, when wire having a diameter of 30 xcexcm or 20 xcexcm was employed, a further reduction in power consumption was possible.
Nevertheless, although momentary opening/closing of the valve was possible, a problem arose in that a leakage of approximately one to two drops a minute could not be prevented. Thereafter, as a result of a detailed discussion of this problem, it was confirmed that the ink leakage was the result of one or more of the following factors.
(1) A sealing gap was opened between the case and the drive shaft when the surface of the case was scratched during deep-drawing and minute raised and recessed portions were formed.
(2) A sealing gap was opened between the drive shaft and the case when the surface of the drive shaft was scratched during cold forging and minute raised and recessed surface portions were formed.
(3) A sealing gap was opened between the rubber seal and the drive shaft when the surface of the rubber seal, while being formed around the drive shaft, was slightly scratched and raised and recessed surface portions were formed.
Through a discussion to ascertain the feasibility of using deep-drawing to form an extremely smooth surface, it was ascertained that it was impossible to obtain a case having a smooth surface when the deep-drawing process was used for the case. This was because during deep-drawing slight scratching of the metal die that was used occurred, and because it was found that when the process was used for continuous production, an uncountable number of 10 xcexcm scratches occurred in a period during which deep-drawing was repeatedly performed approximately 1000 times. Further, since during cold forging the metal die that was used was deformed, similar scratches occurred earlier than they did during the deep-drawing process, i.e., after the cold forging had been repeated 600 times.
In addition, since a gap appears between metal seals based on an error in the size precision, even when the case and the drive shaft have mirror faces, a slight gap is opened by a difference in the friction developed in the oblique direction and ink leakage occurs.
Therefore, a method was employed whereby a rubber member was used for sealing, and rubber seal was integrally formed with the drive shaft using compression junction, so that the drive shaft was sealed within the case. However, even with this method, obtaining a complete seal was impossible, and a slight ink leakage occurred.
As a result, it was found that when a scratch was formed inside a metal case, and when the surface of the rubber seal was also slightly scratched and the rubber was flat, deformation of the rubber seal could not pinch-off divide the scratch and the slightly raised and recessed portion by pinch-off division.
As a result of a discussion, to resolve this problem it was decided to either apply a flat resin coating to cover the scratch at the sealed portion of the metal case, or to change the shape of a bobbin case and form the sealed portion as a mirror face for the bobbin case.
Furthermore, the following means was employed as a method for resolving the problem posed by a scratch in the rubber seal and for increasing a pinched-off and deformed portion. To resolve the problem or to reduce the size of a scratch in the rubber seal, a flat pressing formation was not used to form the rubber, but instead, an emigration compression formation was employed to provide a mirror face for the rubber seal.
According to the method for increasing the pinched-off and deformed portion, when the sealing portion of the rubber seal was crest shaped and a pressing load was imposed to form a seal, the rubber seal portion at the summit of the crest could be easily flattened and the pinched-off and deformed portion increased.
In this manner, a compact, low power consumption solenoid valve could be produced.
When ink was not evacuated from the solenoid valve and the valve was maintained in the sealed state for an extended period of time, the opening and closing of the valve was impossible.
It was found that this was due to pseudo bonding of the rubber seal to the sealing face of the case, a condition occasioned by a reaction between the rubber seal and the ink element. Further, this effect was frequently witnessed when the sealing face of the case was coated with resin.
From these results, pseudo bonding is regarded as a reaction between the rubber seal and the ink element at the sealed face of the case, and impurities released by the two sealing members.
Thus, as a result of a purposeful study, a stable fluororubber was selected and employed as the rubber seal, which at low temperatures releases very few impurities and that neither reacts with organic materials nor swells nor contracts.
Further, the member whereon the sealed face of the case was formed was a resin coated layer, in particular, a coated layer prepared by baking, at a temperature of 300xc2x0 C., polyimido, a stable material that seldom releases impurities when heated.
A resin bobbin composed of polysulfone, which does not contain a smoothing agent or release agent, was employed as a bobbin case integrally formed with the sealed face.
With this arrangement, a small ink supply solenoid valve could be manufactured that could stably be opened and closed, even after it had been sealed for an extended period of time.
A liquid flow path opening/closing device that can resolve the various problems listed above has the following arrangement. That is, according to the present invention, an electromagnetic driven liquid flow path opening/closing device comprises:
a highly permeable drive shaft;
urging force exertion means for impelling the drive shaft in one direction;
a bobbin case within which the drive shaft inside a cylindrical chamber is positioned;
a coil wound around the outer face of the bobbin case;
a pair of highly permeable cases in which the bobbin case around which the coil is wound is stored; and
a liquid flow path, communicating with the cylindrical chamber of the bobbin case wherein the drive shaft is positioned,
wherein the liquid flow path is opened by impelling the drive shaft to counter the urging force exerted by the urging force means.
With this arrangement, an electromagnetic force is generated by supplying an electric signal to the coil, and the drive shaft in the cylindrical chamber of the bobbin case is impelled to counter the urging force exerted by the urging force means while, in this fashion, opening the liquid flow path. With this structure, a compact opening/closing device can be implemented that is appropriate for flow control along the ink route of an ink-jet printer, and that has a mass equal to or less than 10 g and for operation requires only 1.2 W or less.
In the opening/closing device, it is preferable that the portion that is located opposite the direction in which the drive shaft is impelled by the urging force exertion means, and that contacts the drive shaft, be mounted inside the coil, in order to stabilize the shaft driving direction.
The portion to which the drive shaft is impelled by the urging force exertion means is a flat face integrally formed with the bobbin case, and rubber seal is provided at that portion of the drive shaft that is secured to the flat face, so that the liquid flow path is shielded by the flat face and the rubber seal. Or, a preferable arrangement is for the portion to which the drive shaft is impelled by the urging force exertion means to be a smooth face that is coated on the bottom of a recessed portion in one of the highly permeable cases, and for a rubber seal to be provided at that portion of the drive shaft that is secured to the smooth face, so that a seal is provided for the liquid flow path by the smooth face and the rubber seal. With this arrangement, during the drive idle time, the rubber seal attached to the drive shaft is transported to the flat face or the coated smooth face whereat there are no scratches and no raised or recessed portions, to provide preferable shielding for the liquid flow path.
It is preferable that anticorrosive layers that do not adversely react with ink be deposited on the faces of the highly permeable case and the drive shaft that are directly contacted by ink. The anti-corrosive layers can be polyimido evaporation layers or epoxy resin coated layers.
The rubber seal is fluororubber, and the sealing portion is crest shaped. According to this arrangement, when the surface of the rubber seal is scratched sightly and the rubber is flat, or when the rubber seal is deformed by splitting that occurs as a result of the scratch or at raised and recessed portions, and a good seal can not be provided, the problem can be resolved and a better, more complete shield can be provided for the ink flow path.
The highly permeable cases are formed by the deep-drawing of a highly permeable metal plate, and the drive shaft is manufactured by the cold forging of a highly permeable material. Thus, high productivity can be achieved at a low cost.